(let ((x 5)) x)
=> 5
(let ((x (fx+ 1 2))) x)
=> 3
(let ((x (fx+ 1 2))) (let ((y (fx+ 3 4))) (fx+ x y))) 
=> 10
(let ((x (fx+ 1 2))) (let ((y (fx+ 3 4))) (fx- y x)))
=> 4
(let ((x (fx+ 1 2)) (y (fx+ 3 4))) (fx- y x))
=> 4
(let ((x (let ((y (fx+ 1 2))) (fx* y y)))) (fx+ x x))
=> 18
(let ((x (fx+ 1 2))) (let ((x (fx+ 3 4))) x))
=> 7
(let ((x (fx+ 1 2))) (let ((x (fx+ x 4))) x))
=> 7
(let ((t (let ((t (let ((t (let ((t (fx+ 1 2))) t))) t))) t))) t)
=> 3
(let ((x 12)) (let ((x (fx+ x x))) (let ((x (fx+ x x))) (let ((x (fx+ x x))) (fx+ x x)))))
=> 192